He didn’t use him as bait. In that situation even though Elliot was innocent he looked absolutely guilty. The duke had to do something and keep him safe while he figures out the real culprit. The duke showing favor to Elliot actually backfires because now whoever wants to hurt the duke will want to try to get to Elliot first.
oh, its actually, so much worse. there's panels missing in chapter 24 and the duke shamelessly asks him 'do you hate me?' (which the MC obviously has to lie about) and then follows up saying he wants to apologize for the situation and give the MC compensation. But the apology is just him avoiding all responsibility and making excuses for himself about how the MC can't blame because using him as bait was the best way and 'he had no other choice,' and to compensate the MC, he can even pick darlin's punishment! And then when the ML goes into a rant about various ways he could punish darlin 'for' the MC, the MC essentially zones out because he already knew it was the best choice but it still hurt and he hates him regardless. He kind of just asks himself what more he can do here and if he needs to try harder/pretend more (essentially wondering what the ML even wants from him in that situation). Finally, he questions if the ML actually thinks monologuing at him will make everything better ("Do you think if you recite it like a machine, the sadness will suddenly disappear?"). Then the MC pretty much cuts him off and tells him Darlin's punishment doesn't involve him and it's up to the duke's discretion.
Well well.... it can get even worse than that. Wishing the duke gets character development as soon as possible..
Ngl if I was Elliot I would resign the next day ain't no way I can look at my boss the same way again. And the duke didn't even apologize for locking him up and using him as a bait. I would totally loose all feelings.